Farm-worker putting duck in enclosure (4)

I believe the answer is:

peon

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'enclosure' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for peon that I've seen before include "Latin American farm labourer" , "Spanish-American farm worker" , "lowly farm worker" , "Spanish-American farm labourer" , "Spanish-American menial worker" .)

I've seen this clue in The Sunday Times and The Times.

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